1. Field of the Invention
The present invention relates to a curable composition that comprises an oxyalkylene polymer having a silicon-containing group(s) that has a hydroxy group(s) and/or a hydrolyzable group(s) bonded to a silicon atom(s), and can be crosslinked by forming siloxane bond.
2. Description of the Related Art
The oxyalkylene polymer that comprises a silicon-containing group(s) having a hydroxy group(s) and/or a hydrolyzing group(s) bonded to a silicon atom(s), (to be referred to as a reactive silicon group(s) hereinafter) that can be crosslinked by forming a siloxane bond, is disclosed, for example, in Japanese Patent Publication, No. 52-72998 and U.S. Pat. No. 3,971,751.
Its typical example is a polymer represented by the general formula: EQU X".sub.3 Si-(oxypropylene polymer)-SiX".sub.3
[where X" represents a hydrolyzable group such as a methoxy group].
An oxyalkylene polymer having a reactive silicon group(s) cures through forming a siloxane bond (Si--O--Si) between polymers by the action of moisture at room temperature like room temperature curable silicone rubber, and produces a rubber-like cured substance. This cured substance is so excellent in elongation property, strength and adhesiveness that it is used as sealants, adhesives and such.
This polymer may be used, for the purpose of lowering cost, as a composition to be mixed with a filler.
The addition of a filler, however, has been problematic: it increases the weight of the cured substance, and it does not lower the cost as expected.
Although it has been suggested that the addition of glass microspheres may be beneficial, the resulting cured material often has its elastic properties impaired, i.e., reduced elongation property and increased tensile modulus.
It has been disclosed in Japanese Patent Publication, No. 63-191856 that organic hollow microspheres of vinylidene chloride polymer are added to a polyurethane substrate to improve the adhesiveness to the substrate.
The present inventors found that these organic hollow microspheres are capable of affording a light-weight, highly-filled cured substance without degrading the physical characteristics such as elongation property, while providing the advantage of cost reduction.